1. Technical Field
The present invention relates to a measurement apparatus, a test apparatus, and a measurement method. In particular, the present invention relates to a measurement apparatus, a test apparatus, and a measurement method for measuring current flowing through a load.
2. Related Art
When testing a device under test such as a semiconductor circuit, a test apparatus may use a voltage application current measurement test that involves measuring the current flowing to the device under test while a DC voltage is being applied to the device under test, as in, for example, Japanese Patent Application Publication No. 2007-127568 and International Publication Pamphlet No. 2005/116672. When performing the voltage application current measurement test, the test apparatus measures the current by detecting the potential difference between the ends of a sense resistor provided between the power supply section and the device under test.
When a large current flows to the sense resistor due to excess current during the voltage application current measurement test, the potential difference between the ends of the sense resistor is increased. This causes the power supply section in the test apparatus to increase the output voltage to keep the voltage supplied to the device under test constant. However, there is a limit on the voltage that the power supply section can output. Therefore, when the output voltage of the power supply section increases due to an excess current flowing to the sense resistor during the voltage application current measurement test, the output voltage of the power supply section might reach its maximum value. When this happens, the test apparatus cannot continue to supply the constant voltage to the device under test.
One way to solve this problem involves connecting forward diodes in parallel with the sense resistor to limit the potential difference between the ends of the sense resistor. In this way, the test apparatus can control the output voltage of the power supply section to not reach the maximum value. However, since this test apparatus includes the forward diodes connected in parallel with the sense resistor, the circuit size is undesirably large.
Furthermore, with this test apparatus, connecting the diodes to the sense resistor at a plurality of stages increases the voltage tolerance, making it necessary for the current leaked to the diodes during measurement of the current to be decreased. However, such a test apparatus is electrically inefficient because it must be provided with a power supply section in which the voltage allowance (headroom) between the voltage applied to the device under test and the maximum voltage of the power supply section is larger than at least the voltage decrease at the diodes.